The background to the invention will now be set out with reference to the example applications of the authentication of security documents incorporating (typically printed on) a light permeable sheet of substrate material. However, the invention may be applied more generally to the authentication of other items, at least a portion of which has a thickness which is measurable using an optical thickness measurement.
Within this specification and the appended claims, by “security document(s)” we include documents of value, such as bank notes and bearer bonds; payment tokens, such as credit and debit cards and vouchers; certificates and identification documents, such as passports, driving licenses and identity cards. By the authentication of a security document, we refer to verification to a suitable level of certainty, which is typically less than 100%, that a security document originates from a prescribed or authorised source.
It is well known to provide security documents that include security elements, such as magnetic strips, special inks, print which is difficult to reproduce, optical features, such as holograms or diffraction gratings, and tamper-resistant electronic devices. Some security elements are overt to the human eye and some are covert, requiring knowledge of the element or special equipment to detect. Security documents are typically printed onto or embedded into a sheet of substrate material, such as a sheet of an appropriate paper, or plastics material, and it is known to provide apparatus to automatically authenticate documents by detecting security elements which have been introduced into or onto a sheet of substrate material.
However, standalone apparatus suitable for the authentication of security documents at points of sale is only in limited use at the present time. Points of sale may have a UV light source for detecting a fluorescent ink on a bank note, or a pen which does not mark authentic bank notes. These devices do not provide a high technical hurdle to counterfeiters. Points of sale may also have electronic apparatus which authenticates a credit or debit card using a tamper-resistant electronic circuit embedded in the card. However, this apparatus is complex and expensive, requires time to process and a telecommunications link to a remote server, and is not suitable for use in the authentication of bank notes during routine cash transactions.
More sophisticated apparatus for checking the authentication of bank notes is in common use by credit institutions and professional cash handlers for checking bank notes which are to be returned to circulation, but such apparatus is expensive, particularly as it is generally necessary to check for the presence of multiple security features to authenticate a bank note. Cash receiving machines have less sophisticated authentication apparatus as they have to be kept to a relatively low cost.
Some embodiments of the present invention aim to provide authentication apparatus and methods which can be implemented in a reasonably priced, reliable way such as to be suitable for use at a point of sale, or in a cash receiving machine. Some embodiments of the present invention aim to measure new or alternative properties of a security document, such as a bank note, to facilitate automatic authentication of security documents, or to present an additional hurdle to counterfeiters by providing one or more additional features which a counterfeit security document must have in order to be incorrectly determined to be authentic.
The invention makes use of known sheets of security document substrate which are permeable to electromagnetic radiation, for example, transparent in the visible region of the electromagnetic spectrum. It is known to create security documents, such as banknotes, by printing opaque inks onto sheets of transparent plastics substrate material, leaving a transparent window. The resulting window provides an overt security feature which is conspicuous to the human eye. It is known to print, etch or embed additional optical security features, such as optically variable devices formed by diffraction gratings, onto or into the resulting transparent windows, to provide additional overt security features. It is possible to provide automatic authentication apparatus which can determine authenticity from the presence or absence of these additional optical security features, but such apparatus is typically complex and expensive.
Some embodiments of the invention aim to use windows which have been left permeable to electromagnetic radiation (and typically transparent in the visible region of the electromagnetic spectrum) on security documents made from sheets of plastics substrate material which are permeable to electromagnetic radiation (and typically transparent in the visible region of the electromagnetic spectrum), to thereby provide one or more measurable characteristics which can be taken into account when determining whether a security document is authentic.
Some embodiments of the invention aim to provide sheets of substrate material for security documents which are adapted to facilitate authentication by the optical measurement of the thickness of one or more layers within the sheets of substrate material, as well as security documents include the said sheets of substrate material.
The invention also addresses the problem of authenticating products which may be counterfeited, such as alcoholic drinks, watches and other items of jewelry, perfumes, branded clothing, pharmaceuticals and cigarettes. It is well known to provide optically detectable security features, such as holograms, to be incorporated into the packaging of products, or into the products themselves. These optically detectable security features may be detected by the human eye, or by automatic authentication apparatus. However, features which are visible to the human eye can often be duplicated and the automatic authentication apparatus used to detect some known security features can be expensive.
Accordingly, some embodiments of the invention aim to provide alternative or improved methods and apparatus for authenticating products which may be counterfeited.
Furthermore, where overt optical security features are provided in or on products and security documents, they will be apparent to counterfeiters who can then address the problem of trying to reproduce the security feature. Some embodiments of the invention aim to authenticate items, such as products which may be counterfeited, or security documents, by measurement of an optical characteristic which is not readily apparent to the human eye, which may make it difficult for counterfeiters to determine which features are being verified during authentication.